The wireless coverage indoors of a mobile communication system is not so good. This has some reasons; for example, wireless electric waves are difficult to reach the inside of a building and it costs much to set an indoor-typed wireless base station and to make use of it.
Under this situation, a microminiature wireless base station (BTS: Base Transceiver Station) called “Femtocell” has been proposed these days. This BTS is assumed to be used inside a house or office and it conforms to, for example, the W-CDMA (Wideband-Code Division Multiple Access) method, enabling a simultaneous communication for a small number of users (about four users) after forming a small sized cell (femtocell) having a radius of some tens meters. Further, the cost is low.
In order to improve the indoor coverage without raising the operation cost, it is considered that such a small BTS (hereinafter, referred to as a femtocell BTS) is arranged inside a tall building or an underground facility (dead zone) which could not be covered by the existing wireless base station.
Further, a technique of remotely setting an RF (Radio Frequency) unit connected with an existing base station unit via a cable line, is known as a means for improving the coverage of the mobile communication system.    [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-40802    [Patent Document 2] Japanese Patent Application National Publication (Laid-Open) No. 2002-524989    [Non Patent Document 1] “A follow up article on 3GSM, Korea Samsung and NEC exhibit “Femtocell”    [Non Patent Document 2] “Manufacturing Agreement For Zone Gate Low-Cost Residential 3G Access Point”.    [Non Patent Document 3] NTT DoCoMo Technical Journal Vol. No. 1, [online], April, 2007.
Since the femtocell BTS is supposed to be set indoors, the number of the femtocell BTSs being set is expected large. However, there is a limit to the capacity (for example, some hundreds BTSs) in a device which accommodates the base transceiver stations and controls them (RNC: Radio Network Controller). Therefore, it cannot help but increase the number of large-sized expensive RNCs, in order to accommodate a large number of femtocell BTSs (for example, more than some thousands BTSs).
The technique of Patent Document 1 is only a technique for just relaying a signal destined for a mobile station unit from a base station unit, through the RF unit connected with the base station unit via a cable line.